1. Technical Field
The present invention relates to a motor including a control circuit, which is installed such as in automobiles or trucks, and in particular to a brushless-type electric motor as an AC electric motor which is provided with a rotor having an intermediate magnetic pole exerting magnetic characteristics intermediate of an N magnetic pole and an S magnetic pole.
2. Related Art
Three-phase AC motors are used for various purposes. One of the recently suggested three-phase AC motors is provided with annular-shape windings and configured such that the magnetic flux in the motor has its path along the rotor shaft. FIG. 49 is a schematic vertical cross-sectional view illustrating the configuration of such a motor as an example. In the figure, reference Q11 indicates a rotor shaft, reference Q12 indicates N-pole permanent magnets and S-pole permanent magnets mounted on the surface of the rotor, reference Q13 indicates U-phase stator poles, reference Q14 indicates V-phase stator poles and reference Q15 indicates W-phase stator poles. Further, reference Q1A indicates a back yoke portion of a stator magnetic path, reference Q16 indicates an annular U-phase winding provided in the circumferential direction, references Q17 and Q18 indicate annular V-phase windings provided similarly, reference Q19 is an annular W-phase winding provided similarly, reference Q1B is a motor case and reference Q1C is a bearing. FIG. 50 is a linear development view illustrating a circumferential surface configuration of the permanent magnets Q12. In the figure, the circumferential direction corresponds to the horizontal direction in which angle is indicated in mechanical angle. FIG. 50 shows an example of an eight-pole rotor, in which reference Q21 indicates N-pole permanent magnets and reference Q22 indicates S-pole permanent magnets.
FIG. 51 is a linear development view illustrating a circumferential configuration of U-, V- and W-phase stator poles opposed to the permanent magnets of the rotor shown in FIG. 49. The U-, V- and W-phase stator poles Q13, Q14 and Q15 are arranged so as to have a phase difference of 30° in mechanical angle and 120° in electrical angle. Various modifications may be applied to the configuration of the stator poles of the individual phases, which is opposed to the permanent magnets of the rotor. For example, as shown in FIG. 52, the stator poles may each have a rectangular shape. In the figure, reference Q31 indicates U-phase stator poles, reference Q32 indicates V-phase stator poles and reference Q33 indicates W-phase stator poles.
Further, as shown in FIG. 53, the stator poles of the individual phases may have a configuration in which trapezoidal shape and rhombic shape are combined. In the figure, reference Q41 indicates U-phase stator poles, reference Q42 indicates V-phase stator poles and reference Q43 indicates W-phase stator poles. In the stator configuration, the phases each have an equal area with a relative phase difference of 120° in electrical angle therebetween. In this case, magnetic flux passing through the stator poles has a value that changes with rotational angle θr of the rotor. The values of the magnetic flux are approximate to a sinusoidal waveform in contrast to a rectangular waveform obtained from the configuration shown in FIG. 52. Thus, the stator configuration shown in FIG. 52 has an effect of reducing torque ripple.
FIG. 54 shows the U-phase winding Q16 among the annular-shape windings of the phases shown in FIG. 49. FIG. 54 shows by (a) a front view, and shows by (b) a side view. In the figure, a reference U indicates one end of the U-phase winding Q16 and a reference N indicates the other end of the U-phase winding Q16. The V-phase windings Q17 and Q18 and the W-phase winding Q19 shown in FIG. 49 also have the same shape as the U-phase winding Q16 shown in FIG. 54.
FIG. 55 is a linear development view illustrating a circumferential configuration of the annular-shape windings of the phases shown in FIG. 49. The U- and V-phase windings Q16 and Q17 shown in FIG. 49 are wound in parallel sharing each of the slots and thus may be combined into a single loop winding. Specifically, the U-phase winding Q16, which is negative, and the V-phase winding Q17, which is positive, may be equivalently replaced by a winding Q71 shown in FIG. 56. However, the current supplied to the winding Q71 is required to be a sum of the currents supplied to the U- and V-phase windings Q16 and Q17.
In this case, the value of the current passing through the slots is the same between the configurations shown in FIGS. 55 and 56. Thus, electromagnetically, these configurations are equivalent. The combined winding as shown in FIG. 56 is advantageous in that the winding is simplified. Further, the phase difference in electrical angle is 60° between the negative U-phase current (−Iu) supplied to the U-phase winding Q16 and the positive V-phase current Iv supplied to the V-phase winding Q17. Accordingly, an effective value of the sum of these currents (−Iu+Iv) is smaller by a factor of 0.866 than that of the currents before being combined. In terms of Joule heat of the windings, the sum corresponds to the square of the effective value and thus is smaller by a factor of 0.75 than that of the currents before being combined, thereby reducing the generated heat by 25%.
Similarly, the V- and W-phase windings Q18 and Q19 shown in FIG. 55 may be replaced by a winding Q72 shown in FIG. 56 for simplification. When the windings shown in FIG. 56 are adopted, the motor shown in FIG. 49 turns to a three-phase AC motor with two windings.
FIG. 57 shows an example of connection with a three-phase AC inverter.
A current (−Iu+Iv) is supplied to an end 45E of the winding Q71, while a current (−Iv+Iw) is supplied to an end 45F of the winding Q72. On the other hand, a current (−Iw+Iu) is supplied to a connecting point 45G between the windings Q71 and Q72. When the three-phase currents Iu, Iv and Iw have a phase difference of 120° therebetween and form sinusoidal waves of the same amplitude, the currents (−Iu+Iv), (−Iv+Iw) and (−Iw+Iu) will have a phase difference of 120° therebetween and will form sinusoidal waves of the same amplitude. References 451, 452, 453, 454, 455 and 456 indicate transistors configuring the three-phase inverter. References 457, 458, 459, 45A, 45B and 45C indicate diodes connected in parallel with the respective transistors.
It should be noted that JP-B-3944140 discloses a motor having a configuration as shown in FIG. 49. Also, JP-B-4007339 discloses a motor in which the windings Q16, Q17, Q18 and Q19 of the motor shown in FIG. 49 are configured by the simplified windings Q71 and Q72 as shown in FIG. 56.
As described above, a motor as shown in FIGS. 49 and 56 has a simple configuration including windings having an annular-shape. However, since such a motor is required to be applied with three-phase AC voltages and currents, the control circuit has a configuration as shown in FIG. 57, requiring six transistors. Thus, such a motor raises a problem of cost and size. Further, as to the paths of the currents of the three phases, two transistors are connected in series to a DC power source 2E to supply current to the windings. Accordingly, the heat generated due to the voltage drop of the transistors is desired to be improved and reduced.
In recent years, motors are mass-produced, which are used for household electrical appliances, accessories of automobiles and the like. For example, a motor having a size of about 50 mm in diameter is produced by realizing a technique of incorporating a power source for driving the motor, a control circuit, an inverter and the like into a single semiconductor chip smaller than 10 mm×10 mm, and integrally incorporating the semiconductor chip into a part of the motor.
Thus, reduction in both of the cost and the size of a motor system is underway. Accordingly, various techniques are sought for, such as circuit technique, signal detection technique, temperature-change-handling technique, and motor integration technique, which are dedicated to the realization of the reduction. For example, such techniques include a so-called sensorless control technique that can eliminate the use of a position-detection sensor, or a current detection technique that can reduce the size and cost of a device and cause only a small load due to generated heat.
In such applications as various types of fans used near the ears of persons, motors are required to be quite silent. In this way, motor characteristics contributing not only to reducing size and cost but also realizing high-level motor systems are increasingly sought for.